Expanded polyester polymers, i.e. polyester foam or sponge, are of major importance for a large number of applications related to e.g. insulation against temperature gradients, noise shielding, vibration damping, lightweight construction etc. However, they are basically very sensitive versus decomposition in regard to e.g. hydrolysis or oxygen initiated combustion due to their organic nature caused by the polymer backbone, and due to the fact that hetero atoms having an additional negative effect on stability, such as oxygen, are part of the polymers. What makes the situation even worse is the fact that cellular polyesters are of course weaker than massive material, the surface is much higher, thus, more accessible for aggressive substances, and air/humidity is already available in the cells in case of ignition or alkali or acid attack. Therefore, polyesters basically are easily flammable and tend to continue burning once ignited, and they will continue decomposition by hydrolysis once bond cleavage has taken place. Different efforts have been taken to improve the stability of the polymer compounds themselves, such as the mixing of halogenated and non-halogenated flame retardants, non-combustible fillers etc. into the compound. However, as the manufacturing process of polyester foams is a reactive foaming process (see e.g. EP 0866089, U.S. Pat. No. 5,288,764, JP 5117501, JP 62004729, WO 2001051549; JP 8151470 mentions recycled material made to foam) foreign substances may severely impact the expansion or foaming of the polymers as well as other final properties targeted for the intended applications. Additionally, these foreign substances would have to withstand the processing conditions which might be e.g. almost 300° C. when speaking about polyethylene terephthalate. Most of the standard flame retardant agents would not survive these temperatures and decompose during the process. Other, more stable substances such as inorganic fillers, fibres etc., either will negatively influence the chain length of the polymers or the cell structure or simply can not be compounded into the matrix to an extent where a significant effect could be achieved. To overcome these issues some works have been done on the field of coating and lamination technologies where the restriction provided by the processing of the expanded polyester is not given. KR 100701274 discloses a polyethylene terephthalate (PET) carpet layer with phosphorous as flame retardant. In JP 2008201079, JP 10119219, JP 8068164, JP 1261588, GB 2344834, GB1161045, GB 882296 and U.S. Pat. No. 6,066,580 polyester, polyester fibre or polyester/glass fibre lamination is used to protect the more flammable foam core consisting of other polymers; GB 2222185 claims this system as a kind of “melt-away” fire protection; GB 2122232 is discussing a treatment of foam or its protective layers with halogen/antimony compounds. JP 2006077551 among others is dealing with polyester fibres as an internal flame protection, but covered by a metal foil and using adhesives to bond the layers together. The metal, mainly aluminium, foil indeed is a rather widespread method, see e.g. in JP 2215521, JP 4347252, JP 8199709, U.S. Pat. No. 4,459,334, CH 650196 etc. However, these multilayer methods bear some source for failure, such as the additional uncertainties provided by the necessary adhesive (flammability, durability, compatibility etc.). DE 10117177 mentions a PET foam window sill where the surface is closed for decorative purposes by melting it, but no other measures or benefits are provided, same for JP 6170999 where a polyester (namely PET) layer is coextruded on a polyester foam core for providing a thermoformable board. The possibilities of the combinations of some of the a.m. methods are not thoroughly understood, though. This, however, is essential for developing materials that will be able to fulfil nowadays requirements concerning approvals: e.g. flammability test related certifications within the building industry become more and more global, but also more precise and application-related and therefore more challenging (e.g. ASTM E-84 “tunnel burn test”, UL 94 “horizontal/vertical burn”, EN 13823 “round corner burn test”, FM “room burn test”).